Starch is one of the principle and most abundant carbohydrates. It is formed in plants as a result of photosynthesis and constitutes a source of energy for a variety of organisms including man. The world production of starch is estimated to be 18 million tons, about 50% of that amount is intended for use in foods where starch helps to improve the functional properties of products and provides a source of many oligosaccharides. Starch can also be used in many ways other than a foodstuff such as in glues, coatings sizings and flocculating agents chemicals and building materials.
The industrial use of starch is based on its unique chemical and physical characteristics. Starch can be used in a variety of different ways including as intact granules as swollen granules as a dispersion, as a film, or after conversion to a mixture of oligosaccharides.
Starches can be modified in various ways to render them more suitable for use in the food, paper, textile, soap, laundry cosmetic and pharmaceutical industries. Generally starch is modified by physical, chemical or enzymatic means to acquire particular properties. Physical modifications may be induced by mechanical forces, and/or by hydrothermal treatments that lead to partial or total reorganization of the granular structure. The nutritional and physical properties of physically-modified starch is different from those of the starting material. For example, the complete disorganization of the starch granular structure, which is insoluble in cold water, leads to a form of starch that is highly soluble in cold water. The degradation of amylose by shear leads to the formation of easily digestible oligosaccharides. C. Mercier, Staerke, 29:48 (1977). During thermal treatment of starches or during simple prolonged storage, a number of significant changes occurs that are usually described as "retrogradation". In general, retrogradation is a crystallization process that can be detected by X-ray diffraction. It is brought about by the strong tendency of starch hydroxy groups to form hydrogen bonds with adjacent starch molecules. The changes taking place during retrogradation have a major impact on texture and digestibility of starch-containing food products. Retrogradation is an important factor in the staling of bread and in the texture changes of most starch-containing foods.
Retrogradation of starches has been studied by a variety of techniques including X-ray diffraction, differential scanning calorimetry, and measurements of shear modules. M. J. Miles et al., Carbohydrate Research, 135:271 (1985.) A study of the structure of retrograded amylose revealed that it is composed of crystalline, double-helical regions that interlock with amorphous regions. The formation of crystalline regions increases the rigidity of the granules and reinforces the amylose matrix. The amorphous regions can be hydrolyzed by a number of acids and by enzymes such as alpha amylases, leaving the crystalline regions intact. Hence, retro gradation results in an overall increase in resistance of the starch to the hydrolysis by glucosidic enzymes. S. G. Ring. J. M. Gee M. Whittam, P. Orford and, I. T. Johnson, Food Chemistry, 28:97 1988.
Liquefaction (partial hydrolysis) and saccharification (conversion of liquified starch into glucose) of starch-containing materials by enzymes have become increasingly more important than traditional acid-catalyzed hydrolysis. Among other advantages, enzyme technology provides higher yields, significantly improves product quality and reduces energy consumption. Oligosaccharides Produced by enzymatic hydrolysis can be used in a variety of applications. For example, maltooligosaccharides produced from starch by hydrolysis with alpha amylase can be used in adhesives and in food applications such as syrups, flavor encapsulation., texture control, binding agents, and gels.
Despite a considerable effort directed towards the utilization of enzymes in the starch industry in recent years, there are still few enzyme-derived starch-based products on the market That is particularly evident in the area of low calorie foods. Until recently, starch was thought to be completely hydrolyzed and adsorbed from the small intestine of man. This assumption was based on the fact that the amount of amylase in the human pancreas exceeds the amount that is necessary for complete hydrolysis of the starch consumed. H. N. Englyst and G. T. Macfarlane, J. Sci. Food Agric., 137:699 (1986). Physical modification of starch may result in a product that is resistant to digestion in the small intestine. S. G. Ring et al., Food Chemistry, 28:97 (1988). Thus the development of low-calorie starch-based products is now of considerable interest.